Fig. 9

The crystal structure of the CghA–Sch 210,972 complex and engineering of CghA to generate a mutant capable of generating the unnatural exo adduct [39]. a The structural arrangement of the amino acid residues in the active site of the wild-type (WT) CghA (carbon atoms colored in green) that interact directly with the bound product Sch 210972 (carbon atoms colored in yellow) as observed in the crystal structure of the CghA–Sch 210972 complex. The nitrogen and oxygen atoms are colored in blue and red, respectively. b Apparent turnover rates of the conversion of a simplified substrate analog by the WT CghA and its mutants for the formation of the endo and exo adducts. c The amino acid residues (carbon atoms colored in blue) in the active site of the WT CghA in the vicinity of the bound Sch 210972. The sulfur atom is colored in yellow. d The amino acid residues (carbon atoms colored in blue) mutagenized within the active site to shift the diastereoselectivity of the Diels–Alder reaction from endo to exo. e Schematic illustrations of the interactions between the side chain groups at residues 242 and 257 and the bound transition state (TS) molecule, indicating the potential steric crashes that can determine the stereoselective outcome of the cycloaddition reaction